Methods for separating solid particles from a liquid mixture based on their magnetism or magnetization have been known. For examples, U.S. Pat. No. 3,010,915 discloses magnetic separation of a reduced nickel-kieselguhr catalyst through a magnetic separation zone. U.S. Pat. No. 5,190,635 discloses a separation method of more magnetically active, older, less catalytically active particles from the selective, higher metals-containing catalytic particles, and a rare earth roller-belt magnetic separation unit operates on a side stream of the catalysts. U.S. Pat. No. 4,021,367 discloses separating magnetic nickel catalyst through a continuously moving magnetic field produced with at least two discs rotating on a common shaft and immersed into the liquid suspension, and the collected magnetic catalyst is removed by slanted doctor blades.
Magnetic or magnetizable ingredients have been added to the solid particles to add the magnetism and facilitate their subsequent removal from or retention in the liquid mixture. U.S. Pat. No. 5,171,424 discloses continuously adding one or more heavy rare earth additives as the magnetic hook to the reaction feedstock so that they accumulate on aged catalyst and facilitate the removal of aged catalyst by a magnetic roller belt separator. U.S. Pat. No. 5,538,624 discloses selective magnetic retention of high-cost specialty additives by incorporating into the additives selective magnetic moieties including manganese, heavy rare earth oxidation, and superparamagnetic iron to facilitate their retention and recovery of the additives through a roller belt magnetic separator.
Apparatus for magnetic separation has been known for ages. The roller belt magnetic separator has been used to separate aged fluid catalytic cracking (FCC) catalysts. U.S. Pat. No. 1,390,688 discloses passing liquid through inclined aluminum plates in a magnetic zone to accomplish the magnetic separation of nickels therefrom. U.S. Pat. No. 2,348,418 discloses a magnetic separator having a revolving iron magnetic armature surrounded by field core; the magnetic catalysts are collected on the armature and removed by scraper, and discharged.
The above-mentioned methods of separation are burdensome, and the apparatus does not operate efficiently. These prior separation processes need to be interrupted to collect the recovered magnetic material, and then resumed after the batch collection. Thus, the time for recovery is prolonged, and the rate of recovery or removal is correspondingly reduced.
Chinese Patent No. 02106745.7 discloses a permanent magnetic pair-rollers separator for continuous separation of magnetic particles. The magnetic particles in liquid material are collected and released through rolling of round pair-rollers with same diameter. Since the liquid material touches dam-board firstly after it enters rectangular case and then flows to the rollers on the left and right side for collecting and there is no fixed discharge pipeline, the flowing direction of the liquid after separation is hard to be controlled. The efficiency of separation is relatively low, which influences the continuity of the reaction.